Morphological variation along the sea-land gradient: trees in a subtropical maritime woodland

Abstract

As long-lived sessile organisms, trees demonstrate morphological variability in response to the environmental conditions encountered in a particular local habitat. However, the detection of such variation on a small spatial scale may not be straightforward. In this study we investigated the morphological variation of trees along the edge–interior gradient of a small subtropical-temperate coastal woodland in Amakusa, western Kyushu, Japan. The woodland was located on a narrow sand-spit surrounded by the sea, thus exposed to intense marine influences. In three dominant tree species, Quercus glauca, Ligustrum japonicum, and Pittosporum tobira, the tendency of multi-stemming was significantly greater on the seaward edge of the woodland and declined towards the interior. Furthermore, tree height and size (cross-sectional area at breast height) declined and canopy openness increased towards the woodland edge. In Q. glauca and L. japonicum, shoot growth was more pronounced in the interior than on the edge (i.e. shorter shoots with wider spacing in the latter habitat). Thus, spatial variation in tree structure manifested clearly as shorter height with greater multi-stemming tendencies and greater canopy openness (more spacing among branches/shoots) towards the woodland edge where more light is available and the effects of sea wind and salt spray are greater.